The Plasma Boundary of Magnetic Fusion Devices

Abstract

Writing a book on The Plasma Boundary of Magnetic FusionDevices is a challenge and few others than Peter Stangeby wouldhave been capable of such a task. Indeed, heat load controlonto plasma facing components or helium ash removal can only beresolved by fully integrating all the physics of fusion. Furthermore, they are among the key issues that remain to besolved for the next step machine on the way to Nuclear Fusionwith magnetic confinement.As the Preface of the book rightly points out, this handbook iswell suited for experimentalists or code scientists who wish tointerpret their results and bring some common sense into acomplex story. Part 1, which includes may problems, will alsobe appropriate to students and those plasma physicists who arenot specialists of boundary physics but wish to capture thephysics of this field of research. The very worthy choice ofputting physics forward, backing at each step the modellingeffort with experimental facts (and vice versa), is performed atthe cost of a rigorous and mathematical analysis. The book alsofalls short of establishing the connection between theengineering issues, such as heat removal in the steady state,and the physics at hand, although the former are clearly theincentive for the present effort in the physics. Anotherweakness of the book is too short a section dedicated toturbulent plasma transport depited its importance in definingthe boundary plasma itself and despite the fact that most of theavailable data are measured in the boundary plasma.In a busy book of more than 700 pages, Peter Stangeby hascovered many years of research, from pioneering work, forinstance sheath physics by Tonk and Langmuir in the late 1920's,to areas that remain the subject of active investigation likedrifts in the boundary plasma. The book is divided into 3 partsof very different footing. Part 1, An introduction to thesubject of the plasma boundary, is the textbook of variouscourses given by Peter throughout the world. In this part, thereader is introduced to many of the concepts and facets of thephysics of the boundary plasma. Part 2, Introduction to fluidmodelling of the boundary plasma, is a review of thetheoretical background and the modelling effort of the boundaryplasma. Rather naturally, Part 3, Plasma boundary research,addresses several issues that are currently the scope ofexperimental, modelling and theoretical investigation. The textis further divided in numerous sections and subsections thatorganise this complex subject in a series of well-definedtopics. The style is in the very spirit of Peter's talks, solively that one can nearly hear him.Part 1, written for the largest audience, is more than half ofthe book (about 380 pages). This part starts with thedefinitions of the Scrape Off Layer (SOL), i.e. that region ofopen field lines that surrounds the magnetically confined plasmaand the sheath, namely the standing shock wave between theplasma and wall material. A third section is dedicated to themost important aspects of atomic physics in the SOL, such asionization of incoming particles and erosion of wall material. The following sections are then dedicated to more and moresophisticated description of the SOL, a long section addressingthe issue of impurity generation and subsequent transport. Part2 of the book deals with modelling issues and is relativelyshort (80 pages). The issue of 1-D versus 2-D models as well asthe intermediate so-called onion skin models are introduced. Most of this part assumes a fluid analysis although some kineticaspects are also included. The most important sections in Part3 are dedicated to currents and drifts in the SOL as well asdivertor detachment.Peter Stangeby thus offers the community of fusion physicists avery precious survey of boundary plasma physics. This effort isall the more welcomed since the previous reference book, theoften quoted Physics of Plasma Wall Interactions in ControlledFusion, edited by D E Post and R Behrisch (Nato ASI series,Plenum Press, N.Y. 1986), was written prior to the ITERinternation project that definitely boosted this field ofresearch.Philippe Ghendrih Association Euratom-CEA sur la Fusion Contrôlée,CEA-Cadarache, F-13108 St-Paul-lez-Durance Cedex, France